Image forming apparatus, exposure apparatus and image forming method

ABSTRACT

The image forming apparatus is provided with: plural image carriers; and plural exposure apparatuses that are arranged corresponding to the plural image carriers respectively. The exposure apparatus has a light emitting element member that exposes the image carrier and is arranged on a substrate. A predetermined exposure apparatus among the plural exposure apparatuses includes a heating unit that heats the substrate, and other exposure apparatus other than the predetermined exposure apparatus does not include the heating unit.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC §119 fromJapanese Patent Application No. 2007-065566 filed Mar. 14, 2007.

BACKGROUND

1. Technical Field

The present invention relates to an image forming apparatus and the likesuch as a printer and a copy machine, an exposure apparatus and an imageforming method.

2. Related Art

In a color image forming apparatus with an electrophotographic type suchas a printer and a copy machine, as an exposure apparatus that is usedat the time of forming color toner images, there is a known apparatusthat is formed by arranging light emitting elements such as LED in themain scanning direction. In such an exposure apparatus, since heat isgenerated at the time of lighting the light emitting elements, asubstrate that supports the light emitting elements elongates andretracts due to an influence of the heat. Therefore, differentdisplacement of the light emitting elements is generated for eachexposure apparatus. When the color toner images are combined, there issometimes a case where color drift is generated.

SUMMARY

According to an aspect of the invention, there is provided an imageforming apparatus including: plural image carriers; and plural exposureapparatuses that are arranged corresponding to the plural image carriersrespectively. The exposure apparatus has a light emitting element memberthat exposes the image carrier and is arranged on a substrate. Apredetermined exposure apparatus among the plural exposure apparatusesincludes a heating unit that heats the substrate, and other exposureapparatus other than the predetermined exposure apparatus does notinclude the heating unit.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiment(s) of the present invention will be described indetail based on the following figures, wherein:

FIG. 1 is a view that shows an entire configuration of a printing systemto which an image forming apparatus according to the first exemplaryembodiment is applied;

FIG. 2 is a view that shows a configuration of the first printer and thesecond printer according to the first exemplary embodiment;

FIG. 3 is a sectional configuration view that shows a configuration ofthe LED printhead (LPH)

FIG. 4 is a plan view of the surface side of the LED circuit substrate(on the rod lens array side);

FIG. 5 is a view that shows an example of the page resist mark (ROF) andthe color resist marks (ROC) formed on the continuous paper;

FIG. 6 is a view that shows flow of the heat in the LED circuitsubstrate;

FIG. 7 is a view that explains a function configuring unit that performsthe print width correction in the printers according to the firstexemplary embodiment;

FIG. 8 is a flowchart that shows an example of the procedure ofperforming the print width correction;

FIG. 9 is a view that shows a state where the heater holding member isattached to and detached from the LPH; and

FIG. 10 is a view that shows a state where, in the LED printhead (LPH)according to the second exemplary embodiment, the heater holding memberis attached to and detached from the LPH.

DETAILED DESCRIPTION

Hereinafter, with reference to the attached drawings, a detaileddescription is given to exemplary embodiments of the present invention.

First Exemplary Embodiment

FIG. 1 is a view that shows an entire configuration of a printing system1 to which an image forming apparatus according to the first exemplaryembodiment is applied. The printing system 1 shown in FIG. 1 isconfigured so as to use a continuous paper P that is continuously formedin a belt shape as an example of a recording medium, and form an imageon the both sides of the continuous paper P. That is, the printingsystem 1 according to the first exemplary embodiment is provided with,from the upstream side in the transportation direction of the continuouspaper P towards the downstream side, a continuous paper supplyingapparatus 300, a first printer 100A serving as an example of the imageforming apparatus that is arranged on the upstream side, a buffer unit200, a front-back reverse unit 500, a second printer 100B serving as anexample of the image forming apparatus that is arranged on thedownstream side, and a continuous paper winding apparatus 400.

The printing system 1 according to the first exemplary embodiment isprovided with a control computer 600 that controls actions of theapparatuses configuring the printing system 1. The control computer 600is connected to the continuous paper supplying apparatus 300, the firstprinter 100A, the second printer 100B, and the continuous paper windingapparatus 400 through a communication network 700.

In the continuous paper supplying apparatus 300, a continuous paper roll310 around which the continuous paper P is wound, is installed so as tosupply the continuous paper P to the first printer 100A.

The first printer 100A prints an image on a front surface of thecontinuous paper P that is supplied from the continuous paper supplyingapparatus 300 on the basis of image data that is sent from the controlcomputer 600.

The buffer unit 200 transports the continuous paper P of which, in thefirst printer 100A, a printing processing is performed on the frontsurface side towards the second printer 100B, while holding apredetermined amount of the continuous paper P. That is, in the bufferunit 200, as a transporting roll, an upstream side hanging roll 201, atension roll 202 that is installed movably in, for example, the up anddown direction (the arrow direction), and transports the continuouspaper P while giving a predetermined tensile force to the continuouspaper P, and a downstream side hanging roll 203 are arranged. Thecontinuous paper P is successively transported from the upstream sidehanging roll 201 to the downstream side hanging roll 203 through thetension roll 202 (201→202→203). As a result, a loop that is to hold apredetermined amount of the continuous paper P within the buffer unit200 is formed in the continuous paper P. Such a loop of the continuouspaper P is formed, and the tension roll 202 is moved in the up and downdirection corresponding to a change in the tensile force of thecontinuous paper P so that a big change in the tensile force of thecontinuous paper P is suppressed. Thereby, between the first printer100A and the second printer 100B, tear of the continuous paper P causedby the excessively increased tensile force of the continuous paper P, ordisplacement in the transportation direction of the continuous paper Pand wrinkles in the continuous paper P caused by looseness of thecontinuous paper P is suppressed.

The front-back reverse unit 500 reverses the front and the back surfacesof the continuous paper P and supplies the continuous paper P to thesecond printer 100B. That is, in the front-back reverse unit 500, afront-back reverse roll 501 that is arranged with inclination of 45degrees in the transportation direction of the continuous paper P isprovided. By transporting the continuous paper P while hanging thecontinuous paper P with the front-back reverse roll 501, the front andthe back surfaces of the continuous paper P is reversed. Therefore, thetransportation direction of the continuous paper P that already passesthrough the front-back reverse unit 500 is changed by 90 degrees.Consequently, the second printer 100B is arranged in the direction with90 degrees displacement from the first printer 100A.

The second printer 100B is configured similarly to the first printer100A. On a back surface of the continuous paper P of which, in the firstprinter 100A, the printing processing has been performed on the frontsurface, the image is printed on the basis of the image data that issent from the control computer 600.

The continuous paper winding apparatus 400 winds the continuous paper Pof which, in the second printer 100B, the printing processing has beenperformed on the back surface around a winding roll 410.

It should be noted that in the printing system 1 according to the firstexemplary embodiment, the first printer 100A forms the image on thefront surface of the continuous paper P, and the second printer 100Bforms the image on the back surface of the continuous paper P,respectively. However, the printing system 1 may be configured such thatthe first printer 100A forms the image on the back surface of thecontinuous paper P and the second printer 100B forms the image on thefront surface of the continuous paper P respectively.

The control computer 600 outputs the image data to be printed on thefront surface side and the image data to be printed on the back surfaceside at predetermined timing to the first printer 100A and the secondprinter 100B respectively through the communication network 700.Moreover, the control computer 600 outputs control signals that controlactions of the first printer 100A and the second printer 100Brespectively.

The communication network 700 is configured so as to communicateinteractively by using a communication line and a cable, or may beconfigured by, for example, a network such as LAN (Local Area Network),WAN (Wide Area Network) and the like.

In the printing system 1 according to the first exemplary embodiment,under the control of the control computer 600, the first printer 100Aprints a full color image on the front surface side of the continuouspaper P that is supplied from the continuous paper supplying apparatus300. The continuous paper P of which, in the first printer 100A, thefull color image is printed on the front surface side is transported tothe buffer unit 200, and while a predetermined amount of the continuouspaper P is held in the buffer unit 200, the continuous paper P istransported to the front-back reverse unit 500. The front-back reverseunit 500 reverses the front and the back surfaces of the transportedcontinuous paper P and transports the continuous paper P to the secondprinter 100B.

In the second printer 100B to which the reversed continuous paper P istransported, the full color image is printed on the back surface side ofthe continuous paper P. while the page thereof is aligned with the imagethat is printed on the front surface side in the first printer 100A.Thereby, the full color images are formed on the both sides of thecontinuous paper P. The continuous paper P on which the printingprocessing has been performed in the second printer 100B is fed to thecontinuous paper winding apparatus 400 and wound around the winding roll410.

Next, a description is given to the first printer 100A and the secondprinter 100B according to the first exemplary embodiment. In the firstexemplary embodiment, the first printer 100A and the second printer 100Bhave the same configuration each other.

FIG. 2 is a view that shows a configuration of the first printer 100Aand the second printer 100B according to the first exemplary embodiment(hereinafter, simply referred to as a “printer 100”). The printer 100shown in FIG. 2 is an image forming apparatus with, for example, anelectrophotographic type. The printer 100 is provided with, from theupstream side in the transportation direction (an arrow in the figure)of the continuous paper P towards the downstream side, a papertransporting unit 20 that transports and drives the continuous paper P,and four image forming units, that is, a C-color image forming unit 30Cthat forms a toner image of cyan (C), a M-color image forming unit 30Mthat forms a toner image of magenta (M), a Y-color image forming unit30Y that forms a toner image of yellow (Y), and a K-color image formingunit 30K that forms a toner image of black (K) on the continuous paperP. On the most downstream part, a fixing unit 40 that fixes the colortoner images is provided.

In the paper transporting unit 20, from the upstream side to thedownstream side in the transportation direction of the continuous paperP, aback tension rolls 24, an aligning roll 22, a main drive roll 21 anda paper transportation direction changing roll 25 are arranged.

The main drive roll 21 has a function of nipping the continuous paper Pwith a predetermined pressure, receiving drive from a main motor (notshown in the figure) that is arranged in the paper transporting unit 20,and feeding the continuous paper P at a predetermined transportationspeed. The aligning roll 22 has a function of cooperating with a guidingmember 23 which is in a partially cylindrical shape, and constantlykeeping a transportation route of the continuous paper P on the upstreamside of the main drive roll 21. The back tension rolls 24 have afunction of rotating at a lower speed than that of the main drive roll21 and giving the tensile force to the continuous paper P on theupstream side of the main drive roll 21. The paper transportationdirection changing roll 25 is a driven roll that is driven by windingand hanging the continuous paper P and has a function of changing thetransportation direction of the continuous paper P that is fed from themain drive roll 21 to the direction towards the K-color image formingunit 30K.

Each of the C-color image forming unit 30C, the M-color image formingunit 30M, the Y-color image forming unit 30Y, and the K-color imageforming unit 30K (hereinafter, also collectively referred to as an“image forming unit 30”) is provided with a photoconductor drum 31serving as an image carrier, an electrically charging device 32 thatelectrically charges a surface of the photoconductor drum 31 at apredetermined potential, a LED printhead (LPH) 33 serving as an exampleof an exposure apparatus that exposes the surface of the photoconductordrum 31 on the basis of the image data, a developing device 34 thatdevelops an electrostatic latent image formed on the surface of thephotoconductor drum 31 by each of the color toners, a transfer device 35that transfers the toner image formed on the surface of thephotoconductor drum 31 to the continuous paper P, and a pair of transferguiding rolls 36 and 37 that are arranged on the upstream side and thedownstream side of the transfer device 35 respectively, and press thecontinuous paper P onto the photoconductor drum 31.

Further, the C-color image forming unit 30C is provided with a pageresist mark reading unit 38 that reads a page resist mark (describedlater) for aligning the pages formed on any one of the front surface andthe back surface of the continuous paper P or on both the front surfaceand the back surface, and outputs a timing signal. The K-color imageforming unit 30K is provided with a color resist mark reading unit 39that reads a color resist mark (described later) for aligning the colorimages formed on the surface of the continuous paper P, and outputs thetiming signal and reading position data.

The fixing unit 40 is provided with a flush fixing device 41 that fixesthe color toner images formed on the continuous paper P to thecontinuous paper P by a luminous body such as a flush lump in anon-contact state, tensile force giving roll members 42 that give thetensile force to the continuous paper P on the downstream side of theflush fixing device 41, an aligning member 43 that corrects the route ofthe continuous paper P in the width direction on the downstream side ofthe tensile force giving roll members 42, and tension rolls 44 that nipthe continuous paper P in the vicinity of an outlet, rotate at a higherspeed than the transportation speed of the continuous paper P, and givesthe tensile force to the continuous paper P.

Further, the printer 100 is provided with a comprehensive controller 50that controls an entire action of the printer 100, a paper transportingcontroller 60 that controls the paper transporting unit 20, a C-colorimage forming controller 70C that controls an action of the C-colorimage forming unit 30C, a M-color image forming controller 70M thatcontrols an action of the M-color image forming unit 30M, a Y-colorimage forming controller 70Y that controls an action of the Y-colorimage forming unit 30Y, a K-color image forming controller 70K thatcontrols an action of the K-color image forming unit 30K, and a fixingcontroller 80 that controls an action of the fixing unit 40.

The paper transporting controller 60, the C-color image formingcontroller 70C, the M-color image forming controller 70M, the Y-colorimage forming controller 70Y, the K-color image forming controller 70K,and the fixing controller 80 are comprehensively controlled by thecomprehensive controller 50.

In the printing system 1 according to the first exemplary embodiment,when the printing system 1 is started, the image data for the frontsurface side and the image data for the back surface side are inputtedfrom the control computer 600 to each of the comprehensive controllers50 of corresponding one of the printers 100 through the communicationnetwork 700. The comprehensive controller 50 divides the inputted imagedata into image data respectively corresponding to the C-color, theM-color, the Y-color and the K-color, and sends the C-color image data,the M-color image data, the Y-color image data, and the K-color imagedata to the C-color image forming controller 70C, the M-color imageforming controller 70M, the Y-color image forming controller 70Y, andthe K-color image forming controller 70K respectively.

In synchronization with the inputting of the image data to thecomprehensive controller 50, the comprehensive controller 50 controlsthe paper transporting unit 20 through the paper transporting controller60 and further controls the fixing unit 40 through the fixing controller80 so as to transport the continuous paper P at a predeterminedtransportation speed while giving a predetermined tensile force to thecontinuous paper P.

Under the control of the comprehensive controller 50, the C-color imageforming controller 70C, the M-color image forming controller 70M, theY-color image forming controller 70Y, and the K-color image formingcontroller 70K (hereinafter, collectively referred to as a “color imageforming controller 70”) control formation of each of the color tonerimages in corresponding one of the color image forming units 30.

That is, in the color image forming units 30, under the control of thecolor image forming controller 70, the photoconductor drum 31 startsrotation, and the surface of the photoconductor drum 31 is electricallycharged by the electrically charging device 32 at a predeterminedpotential (for example, −500V). Further, by exposure by the LPH 33 thatemits light on the basis of the color image data, the electrostaticlatent image is formed. The electrostatic latent image on thephotoconductor drum 31 is developed by the developing device 34 with thecolor toners to form the color toner image. The color toner image formedon the surface of the photoconductor drum 31 is transferred to thecontinuous paper P by the transfer device 35 and the transfer guidingrolls 36 and 37.

The continuous paper P is successively transported from the C-colorimage forming unit 30C to the K-color image forming unit 30K through theM-color image forming unit 30M and the Y-color image forming unit 30Y(30C→30M→30Y→30K). Thereby, the color toner images are superimposed witheach other, and a full color toner image is formed on the continuouspaper P.

After that, the continuous paper P on which the full color toner imageis formed is transported to the fixing unit 40, and the toner image isfixed to the continuous paper P by the flush fixing device 41. Thereby,in the first printer 100A, the full color image is formed on the frontsurface side of the continuous paper P. In the same way, in the secondprinter 100B, the full color image is formed on the back surface side ofthe continuous paper P.

Subsequently, a description is given to the LED printhead (LPH) 33 thatis provided in the first printer 100A and the second printer 100Baccording to the first exemplary embodiment.

FIG. 3 is a sectional configuration view that shows a configuration ofthe LED printhead (LPH) 33. In FIG. 3, the LPH 33 is provided with abase 61 serving as an example of a supporting body, a LED array 63serving as an example of a light emitting element member, a LED circuitsubstrate 62 that mounts the LED array 63, a drive circuit 68 serving asan example of a drive unit that drives the LED array 63, and the likeare installed, a rod lens array 64 that forms an image with lightirradiated from the LED array 63 on the surface of the photoconductordrum 31, and a holder 67 that shields the LED array 63 and the like fromthe exterior while supporting the rod lens array 64.

The LPH 33 is also provided with a sheet shape heater 65 that isarranged so as to be brought in contact with the LED circuit substrate62 on the front surface side of the LED circuit substrate 62 (the sidewhere the rod lens array 64 is located), serving as an example of aheating unit that heats the LED circuit substrate 62 from the frontsurface side, a heater holding member 66 that integrally holds the sheetshape heater 65 on the rod lens array 64 side, and a thermal conductivesheet 69 that improves thermal conductive efficiency from the LEDcircuit substrate 62 to the base 61 between the base 61 and the LEDcircuit substrate 62.

The LPH 33 is configured movably in the optical axis direction of therod lens array 64 by an adjusting screw (not shown) and also set so thatan image forming position (focal point surface) of the rod lens array 64is located on the surface of the photoconductor drum 31.

The base 61 is formed by a block or a steel plate made of a metal thathas thermal conductivity such as aluminum and SUS. Corresponding to theelongation and retraction of the LED circuit substrate 62 due to heat,the base 61 supports the LED circuit substrate 62 retractility in thelongitudinal direction. Meanwhile, in the width direction, the base 61supports the LED circuit substrate 62 so that a position of the LEDcircuit substrate 62 is not displaced. In the base 61, plural fins 61 aare formed so as to efficiently irradiate heat.

The holder 67 is set so as to support the base 61 and the rod lens array64 and to keep a predetermined optical positional relationship betweenthe LED array 63 and the rod lens array 64. Further, the holder 67 isarranged so as to seal the LED array 63, the drive circuit 68 and theirradiation surface side of the rod lens array 64 by cooperating withthe heater holding member 66, and prevents adhesion of dirt and the likeonto the LED array 63, the drive circuit 68 and the irradiation surfaceof the rod lens array 64 from the exterior.

The heater holding member 66 is formed by the block including the metalthat has the thermal conductivity such as the aluminum and the SUS andintegrally holds the sheet shape heater 65. The heater holding member 66is configured detachably from the LPH 33. When the heater holding member66 is installed in the LPH 33, the heater holding member 66 is arrangedso as to seal the LED array 63, the drive circuit 68 and the irradiationsurface side of the rod lens array 64 by cooperating with the holder 67.At that time, the heater holding member 66 is configured so as not to bebrought in direct contact with the rod lens array 64. That is, at a partof the heater holding member 66 that is opposed to the rod lens array64, a seal member 66 a that has elasticity such as silicone resin isarranged. By filling a gap between the heater holding member 66 and therod lens array 64, the seal member 66 a shields a space where the LEDarray 63, the drive circuit 68 and the irradiation surface of the rodlens array 64 are arranged from the exterior. Since the seal member 66 ahas the elasticity, the heater holding member 66 may be moved relativelyto the rod lens array 64. Therefore, even in the case where the heaterholding member 66 thermally expands due to the heat from the sheet shapeheater 65, a change in the position of the rod lens array 64 due to thethermal expansion of the heater holding member 66 is suppressed and apredetermined optical positional relationship between the LED array 63and the rod lens array 64 is sustained.

Subsequently, a description is given to the LED circuit substrate 62.FIG. 4 is a plan view of the surface side of the LED circuit substrate62 (on the side where the rod lens array 64 is located).

As shown in FIG. 4, on the surface side of the LED circuit substrate 62,for example the LED array 63 including sixty-five LED chips (CHIP1 toCHIP65) in which three-hundred and eighty-four LED serving as an exampleof light emitting elements respectively are arranged in an array shapeis accurately arranged in a line shape so as to be in parallel to theaxial direction of the photoconductor drum 31.

On the one side of arrangement of the LED chips (CHIP1 to CHIP65), thesheet shape heater 65 that heats the LED circuit substrate 62 whilecontacting the LED circuit substrate 62 from the front surface side, anda temperature sensor 104 that measures a temperature of the LED circuitsubstrate 62 are arranged. For example, the sheet shape heater 65 has astructure of covering both faces of thin-layer stainless steel that is aheating element with a polyimide and is formed with thickness ofapproximately 0.15 to 0.2 mm. Along the arrangement direction of the LEDchips (CHIP1 to CHIP65), the sheet shape heater 65 is formed with thelength in the longitudinal direction that is longer than the length ofthe arrangement of the LED chips.

On the other side of the arrangement of the LED chips (CHIP1 to CHIP65),the drive circuit 68 including sixty-five driver chips (DR1 to DR65)provided corresponding to the sixty-five LED chips (CHIP1 to CHIP65)respectively is arranged. Each of the driver chips (DR1 to DR65) andcorresponding one of the LED chips (CHIP1 to CHIP65) that are driven byeach of the driver chips (DR1 to DR65) are connected to each other bybonding wires.

Further, on the front surface side of the LED circuit substrate 62, athree terminal regulator 101 that outputs a predetermined voltage, anEEPROM 102 that stores correction data of a light quantity or the likefor every LED, and a harness 103 that sends and receives a signalbetween the LED circuit substrate 62 and the color image formingcontroller 70 and supplies electric power and the like.

Next, a description is given to alignment of the image that is formed oneach page in the first printer 100A and the second printer 100Baccording to the first exemplary embodiment. The alignment of the imageincludes alignment of the color toner images that is performed withineach of the printers 100 and alignment of the pages that is performed inthe first printer 100A and the second printer 100B so as to alignpositions of the pages of the images formed on both sides. Further, thealignment of the color toner images that is performed within each of theprinters 100 includes alignment in the sub-scanning direction (thetransportation direction of the continuous paper P) and alignment in themain scanning direction (the direction that is orthogonal to thesub-scanning direction). In the alignment in the sub-scanning directionof the first exemplary embodiment, timing for starting the exposure ofthe image in each of the LPHs 33 is adjusted. The alignment in the mainscanning direction is performed by controlling the temperature of theLED circuit substrate 62 of each of the LPHs 33 and adjusting the lengthof the LED circuit substrate 62. The alignment of the color toner imagesis performed on the basis of the color resist mark (ROC), while thealignment of the pages is performed on the basis of the page resist mark(ROF).

In the printing system 1 according to the first exemplary embodiment,for example, the C-color image forming unit 30C that is located on themost upstream side of the first printer 100A forms the page resist mark(ROF) that is the fiducial of the alignment of the pages in the secondprinter 100B. Each of the color image forming units 30 of the printers100 forms the color resist mark (ROC) that is the fiducial of thealignment of the color toner images formed in the image forming units30. It should be noted that a preprinted paper on which the page resistmark (ROF) is printed in advance may be used. In such a case, theC-color image forming unit 30C does not form the page resist mark (ROF).

FIG. 5 is a view that shows an example of the page resist mark (ROF) andthe color resist marks (ROC) formed on the continuous paper P. The pageresist mark (ROF) and the color resist marks (ROC) shown in FIG. 5 areformed on non-image areas that are located on the both end sides otherthan an image area where the image is formed on the continuous paper Pfor each page. It should be noted that FIG. 5 shows the case where thecolor resist marks (ROC) are formed on one end side of the non-imageareas, however, the color resist marks (ROC) may be formed on both endsides of the non-image areas. In such a case, two color resist markreading units 39 are provided at two places on the both ends in the mainscanning direction.

The alignment of the color toner images for each page that is performedin each of the printers 100 is performed as follows. Firstly, withregard to the alignment in the sub-scanning direction, for example, inthe first printer 100A, a color resist mark of C-color (ROC_C1) isformed in the C-color image forming unit 30C, a color resist mark ofM-color (ROC_M1) is formed in the M-color image forming unit 30M, acolor resist mark of Y-color (ROC_Y1) is formed in the Y-color imageforming unit 30Y, and a color resist mark of K-color (ROC_K1) is formedin the K-color image forming unit 30K individually at predeterminedtiming. The color resist mark reading unit 39 that is arranged in theK-color image forming unit 30K generates a timing signal that showstiming when each of the color resist marks (ROC_C1, ROC_M1, ROC_Y1,ROC_K1) passes through, and sends the signal to the comprehensivecontroller 50.

On the basis of time differences between the timing signal in the colorresist mark of C-color (ROC_C1) and each of the timing signals incorresponding one of the color resist marks of other colors (ROC_M1,ROC_Y1, ROC_K1), the comprehensive controller 50 generates alignmentcorrection data in the sub-scanning direction (the sub-scanning positioncorrection data) at the time of forming the image in the color imageforming units 30 other than the C-color image forming unit 30C. Thegenerated sub-scanning position correction data is sent from thecomprehensive controller 50 to the image forming controllers 70 of thecolor image forming units 30 other than the C-color image forming unit30C, respectively.

On the basis of the sub-scanning position correction data from thecomprehensive controller 50 and a page timing signal described later,the color image forming controllers 70 other than the C-color imageforming controller 70C set timing for starting the image formation inthe sub-scanning direction. Thereby, the alignment of the color tonerimages that are formed in the first printer 100A in the sub-scanningdirection is performed with high accuracy. The same alignment isperformed in the second printer 100B.

Meanwhile, with regard to the alignment in the main scanning direction,for example, in the first printer 100A, a color resist mark of C-color(ROC_C2) is formed in the C-color image forming unit 30C, a color resistmark of M-color (ROC_M2) is formed in the M-color image forming unit30M, a color resist mark of Y-color (ROC_Y2) is formed in the Y-colorimage forming unit 30Y, and a color resist mark of K-color (ROC_K2) isformed in the K-color image forming unit 30K individually atpredetermined timing. The color resist mark reading unit 39 that isarranged in the K-color image forming unit 30K generates readingposition data of the color resist marks (ROC_C2, ROC_M2, ROC_Y2, ROC_K2)and sends the data to the comprehensive controller 50. The comprehensivecontroller 50 generates alignment correction data in the main scanningdirection (the main scanning position correction data: hereinafter, alsoreferred to as the “correction amount”) at the time of forming the imagein each of the color image forming controllers 70 on the basis of theacquired reading position data. The generated main scanning positioncorrection data is sent from the comprehensive controller 50 to each ofthe image forming controllers 70 of corresponding one of the color imageforming units 30. On the basis of the main scanning position correctiondata, the temperature of the LED circuit substrate 62 of the LPH 33described later is controlled so as to adjust the length of the LEDcircuit substrate 62. Thereby, the alignment of the color toner imagesthat are formed in the first printer 100A in the main scanning direction(hereinafter, referred to as the “print width correction”) is performedwith high accuracy. The same alignment is performed in the secondprinter 100B.

The alignment of the pages between the image that is formed in the firstprinter 100A and the image that is formed in the second printer 100B isperformed as follows. As mentioned above, the C-color image forming unit30C that is located on the most upstream side of the first printer 100Aforms the page resist mark (ROF) for each page of the continuous paper P(refer to FIG. 5). The page resist mark reading unit 38 that is arrangedin the C-color image forming unit 30C of the second printer 100B readsthe page resist mark (ROF) on each page, and generates the page timingsignal that shows the timing when the page resist mark (ROF) passesthrough the page resist mark reading unit 38. The generated page timingsignal is sent to the comprehensive controller 50. The comprehensivecontroller 50 sends the page timing signal to each of the image formingcontrollers 70 of corresponding one of the color image forming units 30.

The C-color image forming controller 70C of the second printer 100B setsimage forming timing in the C-color image forming unit 30C on the basisof the acquired page timing signal. Then, on the basis of the set imageforming timing, the C-color image forming controller 70C starts theexposure with the LPH 33.

On the basis of the acquired page timing signal and the sub-scanningposition correction data mentioned above, each of the image formingcontrollers 70 of corresponding one of the color image forming units 30other than the C-color image forming unit 30C sets image forming starttiming and starts the exposure with the LPH 33.

As mentioned above, the second printer 100B according to the firstexemplary embodiment, is configured so that the image forming timing ineach of the color image forming units 30 is set on the basis of thetiming when the page resist mark (ROF) that is formed on the continuouspaper P passes through the page resist mark reading unit 38 of theC-color image forming unit 30C. That is, in the printing system 1according to the first exemplary embodiment, since the exposure starttiming of each of the color image forming units 30 is set on the basisof the position of the page resist mark (ROF) on the continuous paper P,the alignment of the pages with the image that is formed on the frontsurface in the first printer 100A and the image that is formed on theback surface in the second printer 100B is performed with high accuracy.

Subsequently, a description is given to the alignment of the color tonerimages in the main scanning direction (the print width correction) inthe printers 100 according to the first exemplary embodiment.

As mentioned above, the print width correction is performed bycontrolling the temperature of the LED circuit substrate 62 of the LPH33 that is arranged in each of the color image forming units 30 andadjusting the length of the LED circuit substrate 62.

With regard to each LED array 63 that is arranged on the LED circuitsubstrate 62, an arrangement position thereof varies at the time ofmanufacturing. Therefore, among the color image forming units 30,original displacement in the arrangement position of the LED isgenerated. Although each of the LEDs that configures the LED array 63 isa light emitting element with a relatively small heat quantity, forexample, the number of the LEDs is about 25,000 in the case where theLEDs are arranged in the LPH 33 that has the overall length of 530 mmwith a resolution of 1,200 dpi (dot per inch). Therefore, a large heatquantity to the extent that expands the LED circuit substrate 62 isgenerated. Thereby, the displacement in the arrangement position of theLED on the LED circuit substrate 62 is also generated.

Meanwhile, a thermal expansion rate of a print substrate that forms theLED circuit substrate 62 is, for example approximately 10 μm/degree C.in case of the LPH 33 having the overall length of 530 mm. Therefore, inthe LPH 33 having the overall length of 530 mm with the resolution of1,200 dpi, for example, when the temperature is changed by 10 degreesC., the overall length may be changed by approximately 100 μm. Thereby,when temperature amplitude is set to, for example, approximately 10degrees C., the arrangement position of the LED may be adjusted byapproximately 100 μm.

Then, in the printer 100 according to the first exemplary embodiment,the temperature of the LED circuit substrate 62 of the LPH 33 that isarranged in each of the color image forming units 30 is controlled tothe temperature amplitude of approximately 10 degrees C. so as to adjusta thermal expansion amount of the LED circuit substrate 62. Therefore,the print width correction is performed by controlling a displacementamount of the LEDs on the LED circuit substrate 62 of the LPH 33 that isarranged in the color image forming unit 30 so that the displacementamount is substantially the same among the color image forming units 30,and the displacement of the image among the color image forming units 30is reduced. Consequently, generation of color drift is suppressed.

For example, provided that an allowable amount of the displacement ofeach of the color toner images on an image is 150 μm. In such a case, ifthe temperature amplitude of the LED circuit substrate 62 isapproximately 10 degrees C., the arrangement position of the LED may beadjusted by approximately 100 μm. Therefore, when the variations in thearrangement position of the LED array 63 of the LPH 33 that is arrangedin each of the color image forming units 30 at the time of manufacturingare suppressed within a realizable range of +/−125 μm (that is, adifference between the upper limit and the lower limit is 250 μm), theallowable amount of the displacement of 150 μm may be satisfied.

Here, in the LPH 33 according to the first exemplary embodiment, thesheet shape heater 65 that supplies the heat to the LED circuitsubstrate 62 is arranged so as to heat the LED circuit substrate 62while contacting with the LED circuit substrate 62 from the frontsurface side. Meanwhile, the back surface side of the LED circuitsubstrate 62 is arranged so as to be brought into contact with the base61 that has the thermal conductivity through the thermal conductivesheet 69.

As mentioned above, the sheet shape heater 65 heats the LED circuitsubstrate 62 so as to adjust the temperature of the LED circuitsubstrate 62 within a range of the temperature amplitude ofapproximately 10 degrees C., and the print width correction isperformed. Meanwhile, from the LED array 63 that includes the LED chips(CHIP1 to CHIP65) and the drive circuit 68 that includes the driverchips (DR1 to DR65) provided on one side of the arrangement of the LEDarray 63, the heat is also generated at the time of driving the LEDs.The heat that is generated from the LED chips and the driver chipschanges the light quantity of the light that is irradiated from the LEDchips, and unstabilizes a signal processing in the driver chips.Therefore, in the configuration in which the sheet shape heater 65 heatsthe LED circuit substrate 62, a temperature of the LED chips and thedriver chips is excessively increased so that an unstable light quantityand malfunction in the driver chips may be easily generated.

In addition, in the case where a lighting rate of the LEDs isdifferentiated depending on the image area, there is sometimes a casewhere a temperature distribution is generated due to a difference in theheat quantity generated in the longitudinal direction of the LED circuitsubstrate 62. In such a case, when the LED circuit substrate 62 isheated by the sheet shape heater 65, a uniform temperature distributionis not formed in the longitudinal direction of the LED circuit substrate62, and there is sometimes a case where a deformation or a warp isgenerated in the LED circuit substrate 62.

Therefore, it is necessary to efficiently release the heat generatedfrom the LED chips (CHIP1 to CHIP65) and the driver chips (DR1 to DR65)from the LED circuit substrate 62.

Then, in the LPH 33 according to the first exemplary embodiment, thesheet shape heater 65 that supplies the heat to the LED circuitsubstrate 62 is arranged on the front surface side of the LED circuitsubstrate 62, while the back surface side of the LED circuit substrate62 is arranged so as to be brought into contact with the base 61 thathas the thermal conductivity through the thermal conductive sheet 69.Thereby, as shown in FIG. 6 (a view that shows flow of the heat in theLED circuit substrate 62), the heat that is generated from the LED chipsand the driver chips efficiently flows to the base 61 having a largethermal capacity so as to suppress an excessive increase in thetemperature of the LED chips and the driver chips. Consequently, theunstable light quantity of the LED chips and the malfunction of thedriver chips are suppressed. Further, the LED circuit substrate 62 isheated by the sheet shape heater 65 in a state of high uniformity in thelongitudinal direction. Thereby, the deformation and the warp aresuppressed in the LED circuit substrate 62.

Furthermore, the sheet shape heater 65 is arranged on the side portionopposite to the portion where the driver chips (DR1 to DR65) isarranged, across the LED chips (CHIP1 to CHIP65). Therefore, aninfluence of the heat from the sheet shape heater 65 to the driver chipsis reduced, and hence the excessive increase in the temperature of thedriver chips is also suppressed.

As shown in FIG. 6, the sheet shape heater 65 that heats the LED circuitsubstrate 62 is integrally held by the heater holding member 66 from therod lens array 64 side (on the opposite side of the LED circuitsubstrate 62). The heater holding member 66 is formed by the metal thathas the thermal conductivity such as the aluminum and the SUS asmentioned above and is configured so that a part of the heat that isgenerated from the sheet shape heater 65 flows in.

Thereby, the heater holding member 66 also functions as a heatflowing-in unit. Since the heat generated from the sheet shape heater 65also flows into the heater holding member 66, a radical increase in thetemperature of the LED circuit substrate 62 is suppressed. Therefore, astate where the temperature of the LED circuit substrate 62 is overshotexceeding a predetermined range is suppressed. Consequently, a statewhere a radical thermal expansion is generated in the LED circuitsubstrate 62 and the arrangement position of the LEDs on the LED circuitsubstrate 62 is changed for a short time is suppressed. Thereby, in theLPH 33 according to the first exemplary embodiment, a state where thealignment of the color toner images in the main scanning direction istemporarily uncontrollable is suppressed, so that the print widthcorrection is stably performed.

Next, FIG. 7 is a view that explains a function configuring unit thatperforms the print width correction in the printers 100 according to thefirst exemplary embodiment. As shown in FIG. 7, the print widthcorrection is performed under the control of the color image formingcontrollers 70 and the comprehensive controller 50. It should be notedthat, although FIG. 7 specifically shows only the function configuringunit that performs the print width correction within the C-color imageforming unit 30C, the same correction is performed in each of the colorimage forming units 30 other than the C-color image forming unit 30C.

As the function configuring unit that performs the print widthcorrection, the color image forming units 30 are respectively providedwith a temperature detecting unit 71, a heater controller 72 and aheater drive unit 73. The comprehensive controller 50 is provided with acorrection amount calculating unit 51, a memory 52 and a main scanningposition detecting unit 53.

It should be noted that a CPU (not shown in the figure) of each of thecolor image forming controllers 70 reads a program that executesfunctions of the temperature detecting unit 71, the heater controller 72and the heater drive unit 73 from a main memory (not shown in thefigure) into a RAM or the like within each of the color image formingcontrollers 70 to perform various processing. A CPU (not shown in thefigure) of the comprehensive controller 50 reads a program that executesfunctions of the correction amount calculating unit 51 and the mainscanning position detecting unit 53 from a main memory (not shown in thefigure) into a RAM or the like within the comprehensive controller 50 toperform various processing.

In the comprehensive controller 50, the main scanning position detectingunit 53 acquires the reading position data of each of the color resistmarks (ROC_C2, ROC_M2, ROC_Y2, ROC_K2) from the color resist markreading unit 39. The main scanning position detecting unit 53 generatesmain scanning position data with regard to the color resist marks(ROC_C2, ROC_M2, ROC_Y2, and ROC_K2). Then, the main scanning positiondetecting unit 53 sends the generated main scanning position data to thecorrection amount calculating unit 51.

The memory 52 of the comprehensive controller 50 stores an initialdisplacement amount of the LEDs in the main scanning direction for eachof the LPHs 33 that is installed in corresponding one of the color imageforming units 30. The initial displacement amount here is an amount thatis measured in advance at a predetermined temperature (for example, 20degrees C.) as, for example, the displacement amount of the LEDs to adesigned amount at the time of manufacturing. At the time ofmanufacturing the printer 100, the memory 52 stores the initialdisplacement amount of each of the LPHs 33 that is installed incorresponding one of the color image forming units 30 as, for example,4-bit data.

On the basis of the initial displacement amount of each of the LPHs 33that is stored in the memory 52, the correction amount calculating unit51 extracts, for example, the LPH 33 with the largest initialdisplacement amount among the LPHs 33 of the color image forming units30. Further, the LPH 33 with the largest initial displacement amount isset as a reference LPH 33. On the basis of the main scanning positiondata concerning the above reference LPH 33 from the main scanningposition detecting unit 53, the correction amount in the LPHs 33 of theimage forming units 30 other than the reference LPH 33 is calculated.That is, taking the main scanning position data of the reference LPH 33as the reference, a difference from the main scanning position data atthe LPHs 33 of other color image forming units 30 is calculated as thecorrection amount. The calculated correction amount is sent to theheater controller 72 of the color image forming controller 70. Thecalculated correction amount here is an adjusted amount of the length ofthe LED circuit substrate 62 that is to match the position of the LEDsof each of LPHs 33 in corresponding one of the color image forming units30 to the position of LEDs of the reference LPH 33.

Meanwhile, in each of the color image forming controllers 70, thetemperature detecting unit 71 acquires a measured temperature value fromthe temperature sensor 104 on the LED circuit substrate 62. Thereby, thetemperature of the LED circuit substrate 62 is detected and sent to theheater controller 72 as temperature data.

On the basis of the temperature data that is acquired from thetemperature detecting unit 71 and the correction amount that iscalculated in the correction amount calculating unit 51 of thecomprehensive controller 50, the heater controller 72 sets a supplyingamount of electric power to the sheet shape heater 65 that is arrangedon the LED circuit substrate 62.

That is, the heater controller 72 stores a correspondence relationshipbetween a substrate temperature in the LPH 33 and a position changingamount of the LED in, for example, a ROM (not shown in the figure) orthe like serving as an example of a memory, as a table. For example,from a size of the LED circuit substrate 62 in the longitudinaldirection and the thermal expansion rate of a material that constitutesthe LED circuit substrate 62, the correspondence relationship betweenthe substrate temperature of the LPH 33 and the position changing amountof the LED is determined. With using the table, a target temperaturevalue is set from the temperature data and the correction amount, andthe supplying amount of electric power to the sheet shape heater 65 thatadjusts the temperature of the LED circuit substrate 62 to the settarget temperature value is set. The heater drive unit 73 supplies theelectric power that is set in the heater controller 72 to the sheetshape heater 65.

Thereby, the length of the LED circuit substrates 62 in the LPHs 33 ofthe image forming units 30 other than the reference LPH 33 is adjusted,and the alignment of the color toner images in the main scanningdirection (the print width correction) is performed.

Subsequently, a description is given to a procedure of performing theprint width correction in the printers 100 according to the firstexemplary embodiment. FIG. 8 is a flowchart that shows an example of theprocedure of performing the print width correction. The procedure is, asmentioned above, performed under the control of the color image formingcontrollers 70 and the comprehensive controller 50.

As shown in FIG. 8, firstly, the temperature detecting unit 71 acquiresthe measured temperature value from the temperature sensor 104 (S101).The temperature data of the LED circuit substrate 62 is generated fromthe acquired measured temperature value and sent to the heatercontroller 72 (S102).

The main scanning position detecting unit 53 of the comprehensivecontroller 50 generates the main scanning position data on the basis ofthe reading position data of each of the color resist marks (ROC_C2,ROC_M2, ROC_Y2, ROC_K2) that is acquired from the color resist markreading unit 39, and sends the main scanning position data to thecorrection amount calculating unit 51 (S103).

The correction amount calculating unit 51 acquires the main scanningposition data from the main scanning position detecting unit 53 (S104).The initial displacement amount data of each of the LPHs 33 incorresponding one of the color image forming units 30 is acquired fromthe memory 52 (S105). The LPH 33 with the largest initial displacementamount among the LPHs 33 of the color image forming units 30 is set asthe reference LPH 33, and the difference between the main scanningposition data of the reference LPH 33 and the main scanning positiondata of each of the LPHs 33 in corresponding one of other color imageforming units 30 other than the color image forming unit 30 of the LPH33 with the largest initial displacement amount is calculated as thecorrection amount (S106). The correction amount calculating unit 51sends the calculated correction amount in each of the LPHs 33 to theheater controller 72 of the color image forming controllers 70 (S107).

On the basis of the temperature data that is acquired from thetemperature detecting unit 71 and the correction amount data that isacquired from the comprehensive controller 50, the heater controller 72sets the supplying amount of electric power to the sheet shape heater 65(S108). That is, on the basis of the acquired temperature data of theLED circuit substrate 62 and the correction amount data that is acquiredfrom the comprehensive controller 50, the target temperature value ofthe LED circuit substrate 62 is set so that the position of the LEDs onthe LED circuit substrate 62 substantially matches the position of theLEDs on the LED circuit substrate 62 of the reference LPH 33. Then, thesupplying amount of electric power to the sheet shape heater 65 thatadjusts the temperature of the LED circuit substrate 62 to the settarget temperature value is set.

The heater controller 72 sends the set supplying amount of electricpower to the sheet shape heater 65 to the heater drive unit 73. Theheater drive unit 73 drives the sheet shape heater 65 with the setsupplying amount of electric power (S109).

In the LPH 33 according to the first exemplary embodiment, thedisplacement amount of the LED on the LED circuit substrate 62 of theLPH 33 that is arranged in each of the color image forming units 30 iscontrolled to be substantially the same so as to perform the print widthcorrection and reduce the displacement of the image among the colorimage forming units 30. Thereby, the generation of the color drift issuppressed.

As mentioned above, in the LPH 33 according to the first exemplaryembodiment, the heater holding member 66 is configured detachably fromthe LPH 33. Specifically, the heater holding member 66 is configureddetachably from the base 61 serving as the supporting body of the LPH33. FIG. 9 is a view that shows a state where the heater holding member66 is attached to and detached from the LPH 33. As shown in FIG. 9, inthe LPH 33 according to the first exemplary embodiment, since the heaterholding member 66 is configured detachably from the LPH 33, the sheetshape heater 65 corresponding to, for example, a heat generatingcharacteristic of the LPH 33, a temperature characteristic of theprinters 100 in which the LPHs 33 are installed and the like may beselected. Thereby, the generation of the color drift is reduced by theprint width correction with high accuracy. Since a configuration of amain body of the LPH 33 becomes common, a developing efficiency of theLPH 33 is improved.

Here, when the heater holding member 66 is attached to the LPH 33, inorder to improve a heat conduction performance from the sheet shapeheater 65 to the LED circuit substrate 62, a heat conductive sheet ispreferably arranged on a surface where the sheet shape heater 65 isbrought into contact with the LED circuit substrate 62.

Since the heater holding member 66 is easily removed from the LPH 33,manufacturing cost of the LPH 33 is reduced.

As mentioned above, in the print width correction in the printers 100according to the first exemplary embodiment, for example, as shown inthe flowchart of FIG. 8, the reference LPH 33 is set among the LPHs 33of the respective color image forming units 30, and the differencebetween the main scanning position data of the reference LPH 33 and themain scanning position data of each of the LPHs 33 in corresponding oneof other color image forming units 30 is calculated as the correctionamount. With using the calculated correction amount, the length of theLED circuit substrate 62 in each of LPHs 33 in corresponding one of theimage forming units 30 other than the reference LPH 33 is adjusted, andthe alignment of the color toner images in the main scanning direction(the print width correction) is performed.

Therefore, since there is no need for performing the print widthcorrection in the reference LPH 33, there is no need for arranging thesheet shape heater 65 in the reference LPH 33. In the case where theprint width correction is performed by the flowchart of the FIG. 8mentioned above, the reference LPH 33 that is used when the correctionamount is calculated at step 106 is selected in advance. With regard tothe reference LPH 33, the heater holding member 66 that integrally holdsthe sheet shape heater 65 is removed from the LPH 33 in advance. Thereference LPH 33 in the flowchart of the FIG. 8 is the LPH 33 with thelargest initial displacement amount among the LPHs 33 of the color imageforming units 30. Therefore, the LPH 33 with the largest initialdisplacement amount is used while removing the heater holding member 66.Thereby, the LPH 33 is used while the configuration of the main body ofthe LPH 33 becomes common, and the manufacturing cost is reduced byremoving the sheet shape heater 65 from the LPH 33 that does not requireperforming the print width correction.

For example, as the reference LPH 33, the LPH 33 that is installed in apredetermined color image forming unit 30 such as the LPH 33 that isinstalled in the K-color image forming unit 30K may be set in advance.At that time, on the basis of the main scanning position data withregard to the LPH 33 that is installed in the K-color image forming unit30K, the correction amount of each of the LPHs 33 in corresponding oneof the image forming units 30 other than the reference LPH 33 iscalculated. In such a case, since the print width correction is notperformed in the K-color image forming unit 30K, the LPH 33 where theheater holding member 66 integrally holding the sheet shape heater 65 isremoved in advance is used. Thereby, the manufacturing cost is alsoreduced by removing the sheet shape heater 65 from the LPH 33 that doesnot require performing the print width correction.

In addition, in the printers 100 according to the first exemplaryembodiment, the configuration where the four color image forming units30 are arranged is adopted. However, for a user who needs only a blackand white image, the printers 100, each of which is configured by onlythe K-color image forming unit 30K, may be provided. In such a case,although there is also no need for performing the print width correctionin the K-color image forming unit 30K. However, with regard to the LPH33 according to the first exemplary embodiment in which the heaterholding member 66 is detachably configured, the LPH 33 in which theheater holding member 66 is not arranged may be manufactured at a lowcost.

As mentioned above, in the LPH 33 according to the first exemplaryembodiment, the heater holding member 66 that integrally holds the sheetshape heater 65 is configured detachably from the LPH 33. Thereby, thesheet shape heater 65 corresponding to, for example, the heat generatingcharacteristic or the like of the LPH 33 and the printer 100 may beselected. Therefore, in the LEDs among the respective LPHs 33, thealignment is stably performed with high accuracy, and hence thegeneration of the color drift in the formed image is suppressed. Sincethe configuration of the main body of the LPH 33 becomes common, thedeveloping efficiency of the LPH 33 is improved. Further, themanufacturing cost is reduced by removing the sheet shape heater 65 fromthe LPH 33 that does not require performing the print width correction.

Second Exemplary Embodiment

In the LPH 33 according to the first exemplary embodiment, thedescription is given to the case where the heater holding member 66 thatintegrally holds the sheet shape heater 65 arranged so as to be broughtin contact with the LED circuit substrate 62 is configured detachablyfrom the LPH 33. In the LPH 33 according to the second exemplaryembodiment, a description is given to the case where the heater holdingmember 66 that integrally holds the sheet shape heater 65 arranged so asnot to be brought into direct contact with the LED circuit substrate 62is configured detachably from the LPH 33. It should be noted that thesame reference numerals are used for the same configuration as in thefirst exemplary embodiment, and a detailed explanation thereof isomitted.

FIG. 10 is a view that shows a state where, in the LED printhead (LPH)33 according to the second exemplary embodiment, the heater holdingmember 66 is attached to and detached from the LPH 33. The LPH 33according to the second exemplary embodiment is, as shown in FIG. 10, inaddition to the holder 67, provided with a shielding member 90 that isarranged so as to seal the LED array 63, the drive circuit 68 and theirradiation surface side of the rod lens array 64 by cooperating withthe holder 67. The heater holding member 66 that integrally holds thesheet shape heater 65 is attached to and detached from a part where theshielding member 90 is arranged in the LPH 33.

In the LPH 33 according to the second exemplary embodiment, the LEDarray 63, the drive circuit 68 and the irradiation surface side of therod lens array 64 are always set in a sealed state by the holder 67 andthe shielding member 90. Therefore, at the time of attaching anddetaching the heater holding member 66, the adhesion of the dirt and thelike onto the LED array 63, the drive circuit 68 and the irradiationsurface of the rod lens array 64 is suppressed.

At a part of the shielding member 90 that is opposed to the rod lensarray 64, a seal member 66 a that has elasticity such as silicone resinis arranged. By filling a gap between the shielding member 90 and therod lens array 64, the seal member 66 a shields a space where the LEDarray 63, the drive circuit 68 and the irradiation surface of the rodlens array 64 are arranged from the exterior. Since the seal member 66 ahas the elasticity, the shielding member 90 may be moved relatively tothe rod lens array 64. Therefore, even in the case where the shieldingmember 90 thermally expands due to the heat from the sheet shape heater65 through the heater holding member 66, a change in the position of therod lens array 64 due to the thermal expansion of the shielding member90 is suppressed. Thereby, a predetermined optical positionalrelationship between the LED array 63 and the rod lens array 64 issustained.

In the LPH 33 according to the second exemplary embodiment, the sheetshape heater 65 corresponding to, for example, the heat generatingcharacteristic or the like of the LPH 33 and the printer 100 may beselected. Therefore, in the LEDs among the respective LPHs 33, thealignment is stably performed with high accuracy, and hence thegeneration of the color drift in the formed image is suppressed. Sincethe configuration of the main body of the LPH 33 becomes common, thedeveloping efficiency of the LPH 33 is improved. Further, themanufacturing cost is reduced by removing the sheet shape heater 65 fromthe LPH 33 that does not require performing the print width correction.

The foregoing description of the exemplary embodiments of the presentinvention has been provided for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Obviously, many modificationsand variations will be apparent to practitioners skilled in the art. Theexemplary embodiments were chosen and described in order to best explainthe principles of the invention and its practical applications, therebyenabling others skilled in the art to understand the invention forvarious embodiments and with the various modifications as are suited tothe particular use contemplated. It is intended that the scope of theinvention be defined by the following claims and their equivalents.

1. An image forming apparatus comprising: a plurality of image carriers;and a plurality of exposure apparatuses that are arranged correspondingto the plurality of image carriers respectively, the plurality ofexposure apparatuses each having a light emitting element member thatexposes the respective image carrier and is arranged on a substrate,wherein a predetermined exposure apparatus among the plurality ofexposure apparatuses includes a heating unit that heats the substrate,and wherein another exposure apparatus among the plurality of exposureapparatuses does not include a heating unit.
 2. The image formingapparatus according to claim 1, wherein the predetermined exposureapparatus further comprises a heat flowing unit that receives an inflowof heat generated by the heating unit.
 3. The image forming apparatusaccording to claim 1, wherein the heating unit heats a surface of thesubstrate of the predetermined exposure apparatus on which the lightemitting element member is arranged.
 4. The image forming apparatusaccording to claim 1, wherein: the predetermined exposure apparatusfurther comprises a shielding unit that shields the light emittingelement member from the exterior, the heating unit is installed in theexterior, the heating unit heats the substrate through the shieldingunit, the shielding unit receives an inflow of heat generated from theheating unit and integrally holds the heating unit, the substrate issupported by a supporting body, and the heating unit is attached to anddetached from the supporting body integrally with the shielding unit. 5.The image forming apparatus according to claim 1, wherein, in theplurality of exposure apparatuses, the substrate is supported by asupporting body that receives an inflow of heat from the substrate. 6.An exposure apparatus comprising: a supporting body; a substrate that issupported by the supporting body; a plurality of light emitting elementsthat are arranged on the substrate in a line; a heating unit that heatsthe substrate, the heating unit being configured so as to be detachablefrom the supporting body; and a holding member that receives an inflowof heat generated from the heating unit and integrally holds the heatingunit, wherein the heating unit is attached to and detached from thesupporting body integrally with the holding member.
 7. The exposureapparatus according to claim 6, wherein the holding member is installedon the supporting body in a state where the holding member is notbrought into direct contact with an optical member arranged on anoptical path of light irradiated from the light emitting elements. 8.The exposure apparatus according to claim 6, wherein the heating unitheats a surface of the substrate on which the light emitting elementsare arranged.
 9. The exposure apparatus according to claim 6, furthercomprising a shielding unit that shields the light emitting elementsfrom the exterior, wherein the heating unit is supported in theexterior, and wherein the heating unit heats the substrate through theshielding unit.
 10. An image forming method in an image formingapparatus, the image forming apparatus including: a plurality of imagecarriers; and a plurality of exposure apparatuses that are arrangedcorresponding to the plurality of image carriers respectively, theplurality of exposure apparatuses each having a light emitting elementmember that exposes the respective image carrier and is arranged on asubstrate, wherein a predetermined exposure apparatus among theplurality of exposure apparatuses includes a heating unit that heats thesubstrate, and wherein another exposure apparatus among the plurality ofexposure apparatuses does not include a heating unit, the image formingmethod comprising: heating the substrate of the predetermined exposureapparatus among the plurality of exposure apparatuses, and forming animage using the image forming apparatus.
 11. The image forming methodaccording to claim 10, wherein the heating step further comprises:acquiring a temperature of the plurality of exposure apparatuses,acquiring an initial displacement of the plurality of exposureapparatuses, calculating a correction amount, and heating the substrateof the predetermined exposure apparatus among the plurality of exposureapparatuses based off of the calculated correction amount.